The present invention relates to a device for actuating a tilting lever used in sensing sheet-type recording media in document-processing apparatus. In such a device, by means of driving one tilting-lever arm, the tilting lever can be swung about a pivot axis attached to a frame from a first reference position into a second reference position.
Devices of the foregoing type are used in place of paper-thickness sensors. Specifically, in cases where the thickness of a paper stock is not to be determined because, for example, only one piece at a time need be handled in a controlled manner, the presence of a second piece, for example, is not measured but the beginning of the paper strip is measured in order to establish the first line of printing.
In accordance with the prior art, sensing takes place most simply in a purely mechanical manner, with levers and a microswitch (DE-Z Elektronik 1970, No. 1, page 12). This procedure, however, requires an unusually high precision in the case of very thin paper and films, for which reason electromechanical pickups should be more suitable.
From the standpoint of the foregoing prior art, such devices are necessary in multiform printers such as, for example, the Mannesmann-Kienzle D 217 printer. Such printers are used as bank equipment, savings passbook printers or the like. In such printers, the material to be printed on is laid, for example, against a right-hand stop so that sensing of the left edge takes place either by means of movement of the material to be printed on or by means of movement of a carriage supporting or traveling above the material to be printed on. Since such a carriage also supports a print head with print elements, a sensor signal actuated by the paper edge is also used for the beginning of printing.
Known tilting-lever mechanisms are usually realized with springs of the most varied form, the spring tilting via a fulcrum. This principle, however, is subject to the spring having a force corresponding to the distance from the fulcrum, so that there results a spring characteristic with a torque that declines only belatedly and then slowly in relation to the rotation angle of the spring-loaded lever against which the paper edge pushes. For this lever-spring principle it is thus disadvantageous (i) that the actuation force for the lever increases until the tilting of the lever; further, (ii) that the forces and thus the friction on the fulcrum are large as a result of the initial action angle of the spring, making the system sluggish; and (iii) that the arrangement takes up a large amount of space.
It is, therefore, an object of the invention to create an exact switching point even for the lightest weights of paper, which can exert only very slight actuation forces, with abrupt tilting of the lever taking place and therefore a faster system being created.
The foregoing object is achieved in a device according to the invention in which a tilting lever that can be magnetized at least in contact regions is swingably mounted in such a manner that a first tilting-lever arm in a first reference position rests against a first permanent magnet, and in which a second tilting-lever arm in a second reference position rests against a second permanent magnet. The distances from the two permanent magnets to the pivot axis in each case are selected such that unequally large torques exist between the permanent magnets and the tilting-lever arm in each case, in the sense that at least one of the reference positions can be canceled by a smallest possible driving force, and the tilting lever can be abruptly shifted to the other reference position. Via the ratio of the magnet forces as well as their distances from the fulcrum, an abrupt tilting of the tilting lever can advantageously be effected by means of the slightest actuating forces. The device is thus usable even with the thinnest paper, which applies only very slight actuating forces. Furthermore, the system is very fast-acting.
In an embodiment of the invention, the forces of the permanent magnets are selected as a function of the ratio of the pivot axis/first permanent magnet lever arm to the pivot axis/second permanent magnet lever arm, i.e. as a function of the distances. Naturally, switched electromagnets with their magnet core can be used in place of permanent magnets. Moreover, the forces of a permanent magnet are determined in accordance with its dimensions and in accordance with its composite materials.
A special actuation threshold with the additional force of a spring, which is present in any case, and with pulse-like action is achieved in the manner that the first tilting-lever arm in the first reference position rests against the spring-loaded switching element of a microswitch.
A further embodiment of the invention consists in arrangement of the above-described device o the print head carriage of a printer, with the tilting lever being swingably attached parallel to the central plane of motion of the print head carriage and having one tilting-lever arm extending into the path of the recording medium.
The construction of the tilting-lever device for a printer is advantageously undertaken in such a manner that the microswitch is attached to contact the print head carriage on the first tilting-lever arm, and a reset pin is mounted on the print head carriage to contact the second tilting-lever arm. The reset pin is connected to a leg spring and, by means of its end coming in contact with a printer side wall, swings the tilting lever into one reference position.
Further advantages are, moreover, achieved by means of the arrangement of the inventive device on a carriage for an optical reading head or for a magnetic reading or writing device.